Modeling events in racket/scheme

racket simple event video

Make a barracuda image change by rotating it every tick of the clock. This is a first step to using big-bang to create worlds that respond to events. Of course there are problems, technical details, at the beginning... Once you're done with the video, you should be able to

• Make a barracuda switch from regular to mirror image on every tick of the clock
• Define a new function (shrink90 im) that scales im to 90% of its size, and then use your function shrink90 with big-bang to make a barracuda (or any other image you choose) shrink at each tick of the clock

Some relevant non-video resources:

• Sections 6.1 and 6.2 of Picturing Programs
• Guide for Racket's 2htdp/image as well as big-bang documentation.

racket smoother event video

Use big-bang and create a new function rotate-second to get a barracuda to rotate at a speed, and in a direction, suitable for the second-hand of a watch. Nearly tamed that barracuda! After watching the video, you should be able to:

• Create a new speed WORLD-SPEED which is the number of degrees you would need to rotate each second in order to rotate a full 360 degrees in 24 minutes... Some arithmetic required to figure out how many seconds in 24 minutes. Once you've done that, create a new function (rotate24 im) that rotates im a complete 360 degrees every 24 minutes. Now capture an image of planet Earth (a view from the pole might be nice), and use big-bang to make it rotate every 24 minutes... 60 times faster than usual

Some non-video resources:

• Sections 6.1 and 6.2 of Picturing Programs
• Guide for Racket's 2htdp/image as well as big-bang documentation.

racket key event video

That barracuda can be made to rotate about its tail and the timer can be made to stop in response to a keystroke.

racket complex event video

More than just a twirling barracuda — successively-slower twirling pencil and arm — can add live to a simulation

racket transparent event video

Images typically arrive on pale rectangular backgrounds. Make these backgrounds transparent so that you can have one thing in front of the other.